Distilled is the best way to go for extract brews.
The other main key to good Oktoberfest beer is a quality lager yeast, and temperatures as cool as you can get them. W-34/70 yeast is pretty good. So is WLP830, WLP833, WLP820, Wyeast 2308, Wyeast 2206..... The only really mediocre lager choice is WLP820. For temperature, about 50 F is best, and 55-60 F is better than 70 F. If you must ferment warm, stick with W-34/70 which performs okay warm, or consider an altbier yeast like Wyeast 1007 or K-97.